Endoparasiticidal gel composition

ABSTRACT

A homogenous, clear, veterinary gel composition which has a broad spectrum of efficacy against endoparasites over a prolonged period of time and which allows for higher concentrations of a mixture of parasiticidal agents in a single application. This composition is useful for treating and controlling endoparasiticidal infection and infestation in a homeothermic animal.

This application claims priority from copending provisional applicationSer. No. 60/315,104, filed on Aug. 27, 2001, the entire disclosure ofwhich is hereby incorporated by reference.

BACKGROUND OF THE INVENTION

Endoparasiticidal infection and infestation of homeothermic farm andcompanion animals are the cause of significant distress and economicloss to pet owners, animal husbandry men and the like. Efficient controlof said parasites is, therefore, highly desirable and may be achieved bythe administration of suitable endoparasiticidal agents, such asmoxidectin and praziquantel.

Moxidectin is a second-generation endectocide of the milbemycin familyof macrocyclic lactone compounds. The compound is registered andmarketed in various formulations for the control of internal andexternal parasites in farm livestock and companion animals, includinghorses. A 2% oral gel formulation (EQUEST, QUEST) for horses is marketedworldwide. The product is highly effective against a broad-spectrum ofinternal parasites found in horses and ponies.

Equine tapeworms are commonly found in horses throughout the world.Prevalence does not appear to be related to breed or age. The mostcommon species found in surveys has been Anoplocephala perfoliata, withfewer reports involving A. magna and Paranoplocephala mamillana. Untilrecently the horse tapeworm has been considered to be a relativelyharmless inhabitant of the equine gastrointestinal tract. However,recent research has suggested that heavy burdens may predispose horsesto various types of colic, and that the risk increases with the numberof tapeworms present.

Moxidectin, in common with other macrocyclic lactones, does not haveactivity against cestodes, and an alternative class of anthelmintic,such as pyrantel or praziquantel is required for the control of equinetapeworm. Pyrantel is effective when given at double the dose normallyrecommended for control of G.I. nematodes. Praziquantel is ananthelmintic belonging to the pyrazinoisoquinolene class of compounds.It is effective against cestode and trematode infections in animals andhumans. Praziquantel is registered in Australia for the control oftapeworm infections in horses at a dosage of 2.5 mg/kg bodyweight.

Modern endoparasiticidal agents, such as moxidectin and praziquantel,have a wide margin of safety, considerable activity against immature orlarval stages of parasites and a broad spectrum of activity.Nonetheless, the usefulness of any endoparasiticidal agent is limited bythe inherent efficacy of the drug itself, its mechanism of action, itspharmacokinetic properties, features relating to the host animal,features relating to the target parasites and the form ofadministration.

The “ideal” endoparasiticidal administrative form should have a broadspectrum of activity against mature and immature parasites, be easy toadminister to a large number of animals, have a wide margin of safety,be compatible with other compounds, not require long withholding periodsbecause of residues and be economical. Anthelminthic compositions forequidae are described in U.S. Pat. No. 5,824,653; however, saidcompositions are limited in their concentration of effective agents,hence requiring multiple doses for efficacious results. Anthelminthicformulations are also described in U.S. Pat. No. 6,165,987; however,these formulations suitable for oral administration are limited topastes which may make visual identification of contaminants and accurateadministration of measured dosages difficult.

Therefore, it is an object of this invention to provide anendoparasiticidal gel composition which is homogeneous and clear andwhich allows higher concentrations of anthelminthic or parasiticidalagents than formulations known heretofore.

It is another object of this invention to provide a method for thetreatment and control of endoparasiticidal infection and infestation inhomeothermic animals which gives an earlier onset of protection for amore prolonged period of time in comparison to formulations knownheretofore.

These and other features, objects and advantages of the presentinvention will be apparent to those skilled in the art from the detaileddescription set forth hereinbelow, and from the appended claims.

SUMMARY OF THE INVENTION

The present invention provides an endoparasiticidal gel compositionwhich comprises: about 1.0% to 3.5% wt/wt of moxidectin; about 10.0% to15.0% wt/wt of praziquantel; about 4.0% to 24.0% wt/wt of benzylalcohol; about 1.0% to 34.0% wt/wt of ethanol; about 2.0% to 15.0% wt/wtcolloidal silicon dioxide; about 1.0% to 20.0% wt/wt surfactant andabout 35.0% to 61.0% wt/wt of an oil.

The present invention further provides a method for the treatment andcontrol of endoparasiticidal infection and infestation in a homeothermicanimal and a method for the preparation of an endoparasiticidal gelcomposition.

DETAILED DESCRIPTION OF THE INVENTION

Endoparasiticidal agents such as moxidectin and praziquantel may beadministered orally in the form of feed concentrates, feed additives,tablets, oblets, boluses, gels, pastes, or the like or may beadministered parenterally as an injectable. Of the above-mentionedformulation types, arguably the most suitable for ease ofadministration, efficient and effective dosage, and economic andpractical application of the endoparasiticidal agents moxidectin andpraziquantel is an oral gel or paste. Feed additives and feedconcetrates are unsuitable due to the lack of stability of saidendoparasiticidal agents. Tablets, boluses, oblets and drenches arecumbersome to administer to large numbers of animals effectively andparenteral injection is more stressful for the animal and the handler.

A clear, easy-to-use gel form is preferable to a paste because it iseasier on both animals and animal handlers, contamination is readilyvisible and the physical state of the gel readily converts to a liquidupon application of shear or increased temperature. This change from gelto liquid aides in the rapid breakup of the oral gel in the animal'smouth upon its insertion into the oral cavity. This process enables theeasy transit of the dosage form from mouth to the gastrointestinaltrack., i.e., the product is readily swallowed. In contrast, pasteformulations retain their structure and are often spit out of theanimal's mouth. Trials in the field have demonstrated that animalstreated with an active ingredient in gel form exhibit none of the signsof distaste and discomfort, such as head-throwing, tongue-rolling,spitting or not eating, which are characteristic of animals treated withan active ingredient in a paste form.

Surprisingly, it has now been found that moxidectin and praziquantel maybe formulated in a clear, homogenous gel composition. Theendoparasiticidal gel composition of the invention comprises about 1.0%to 3.5%, preferably about 1.5% to 2.5%, more preferably about 1.9% to2.0% wt/wt of moxidectin; about 10% to 15%, preferably about 12.0% to13.0%, more preferably about 12.0-12.5% wt/wt of praziquantel; about4.0% to 24.0%, preferably 18.0% to 22.0%, more preferably about 22.0%wt/wt benzyl alcohol; about 1.0% to 34.0%, preferably about 5.0% to 7.5%wt/wt of ethanol; about 2.0% to 15.0%, preferably about 6.5% to 8.5%wt/wt of colloidal silicon dioxide; about 1.0% to 20.0%, more preferablyabout 3.0% to 6.0% wt/wt of a surfactant; and about 35.0% to 61.0%, morepreferably about 42.0% to 48.0% wt/wt of an oil.

Optional components which may be present in the inventive compositioninclude preservatives such as butylated hydroxytoluene, butylatedhydroxyanisole, sorbic acid, 2-hydroxy-biphenyl, or the like, preferablybutylated hydroxytoluene; thickeners such as ethyl cellulose, xanthumgum, carageenan, hydroxypropylcellulose, hydroxypropylmethylcellulose,or the like, preferably ethyl cellulose; or any conventional inertexcipient commonly used in animal health compositions.

Surfactants suitable for use in the inventive composition includenon-ionic surfactants such as polyoxyethylene sorbitan esters,preferably polysorbate 80, polyethylene glycol 660 hydroxystearate,polyoxyl 35 castor oil, or the like, preferably a polyoxyethylenesorbitan ester, more preferably polysorbate 80.

Oils suitable for use in the inventive composition include propyleneglycol dicaprylate/dicaprate, caprylic/capric triglyceride or the like,preferably propylene glycol dicaprylate/dicaprate.

Advantageously, the clear, homogenous, endoparasiticidal gel compositionof the invention ensures complete and accurate dosing with less stressfor both the animal and the animal handler. Further, the inventive gelcomposition allows for higher concentrations of active ingredients,thereby minimizing the need for multiple dosing. Accordingly, thepresent invention provides a method for the treatment and control ofendoparasiticidal infection and infestation in a homeothermic animalwhich comprises orally administering to said animal an effective amountof a gel composition which comprises: about 1.5% to 3.5% wt/wt ofmoxidectin; about 10.0% to 15.0% wt/wt of praziquantel; about 4.0% to24.0% wt/wt of benzyl alcohol; about 1.0% to 34.0% wt/wt of ethanol;about 2.0% to 15.0% wt/wt of colloidal silicon dioxide; about 1.0% to20.0% wt/wt of a surfactant; and about 35.0% to 61.0% wt/wt of an oil.

Effective amounts may vary according to the general health of theanimal, the degree of infection or infestation, the parasite species,the age of the animal, the organs infected or infested, or the like. Ingeneral, amounts of said gel composition sufficient to provide about 0.3mg/kg to 0.5 mg/kg, preferably about 0.4 mg/kg of moxidectin per bodyweight of the animal and about 2.0 mg/kg to 3.0 mg/kg, preferably about2.5 mg/kg of praziquantel per body weight of the animal are suitable.

Homeothermic animals suitable for treatment in the method of inventioninclude equine, bovine, ovine, swine, caprine, canine, feline or thelike animals, preferably equine animals, more preferably horses.

The present invention also provides a method for the preparation of aendoparasiticidal gel composition which comprises one or more of thefollowing steps:

-   -   1) dissolving a thickener, such as ethyl cellulose, in a mixture        of benzyl alcohol and ethanol to form a solution A;    -   2) suspending praziquantel in an oil, such as propylene glycol        dicaprylate/dicaprate which has been preheated to about 80° C.,        to form a suspension B;    -   3) admixing solution A with suspension B at temperatures ≦50° C.        until a solution C which is homogenous at room temperature is        obtained;    -   4) admixing surfactant and optionally butylated hydroxytoluene        with solution C to form solution D;    -   5) sequentially admixing moxidectin and colloidal silicon        dioxide to solution D to form gel E; and    -   6) mixing gel E under a vacuum to form a clear yellow        endoparasiticidal gel composition that is essentially free of        air.

Several preferred embodiments of the present invention are set forth inthe following examples. These examples are merely illustrative and arenot intended to limit the scope or underlying principles of theinvention in any way. Indeed, various modifications of the invention, inaddition to those shown and described herein, will become apparent tothose skilled in the art from the following examples and the foregoingdescription. Such modifications are also intended to fall within thescope of the present invention, and the appended claims.

EXAMPLE 1

Preparation of Endoparasiticidal Gel Composition A Component Description% wt/wt moxidectin, 90% potency 1.95 praziquantel, 100% potency 12.17benzyl alcohol 22.00 butylated hydroxytoluene 0.08 polysorbate 80¹ 5.00colloidal silicon dioxide 7.50 ethyl cellulose (visc. 4) 0.25 dehydratedalcohol, usp 5.00 Propylene glycol dicaprylate/dicaprate² 45.84(q.s.³)¹CRILLAT ® 4HP, manufactured by Croda Inc., Parsippany, NJ ²Miglyol ®840, manufactured by Condea Vista, Cranford, NJ. ³quantity sufficient tobring total to 100% wt/wt.

Method of Preparation

-   Step 1. Ethyl cellulose is slowly dissolved in a mixture of benzyl    alcohol and ethanol with stirring.-   Step 2. Propylene glycol dicaprylate/dicaprate which has been    preheated to 80° C. is slurried with praziquantel to form a    suspension. When the temperature of the suspension is <50° C., the    solution obtained in step 1 is added, stirring is continued until    the praziquantel is dissolved and the resultant mixture is cooled to    room temperature.-   Step 3. Butylated hydroxytoluene and polysorbate 80 are added to the    mixture obtained in Step 2 with continued stirring.-   Step 4. Moxidectin is added to the mixture obtained in Step 3 with    stirring.-   Step 5. Colloidal silicon dioxide is added to the mixture obtained    in step 4 and mixing under a vacuum using a suitable mixer is    continued until a clear yellow gel, that is free of air, is formed.

EXAMPLE 2

Comparative Field Evaluation of Efficacy of Composition A

In this evaluation, horses with known strongyle infestation are treatedorally with a dose of 0.4 mg/kg moxidectin and 2.5 mg/kg praziquantelgel (Composition A) or a dose of 0.2 mg/kg abamectin and 2.5 mg/kgpraziquantel paste (EQUIMAX® manufactured by Virbac, New South Wales,Australia), or given no treatment (Control). Each treatment consists of10 horses. Fecal egg counts (FEC) are performed and recorded at biweeklyintervals post treatment. The data are averaged. The results are shownin Table I.

TABLE I Comparative Evaluation Fecal Egg Count^(a) Weeks Post TreatmentTreatment 2 4 6 8 10 12 14 Comp. A 0 0 26.7 61.9 173.8 321.0 178.0 EQUI-0 4 288.9 325.0 596.0 880.0 1140.0 MAX ® Control 1246.7 891.1 773.31126.7 2257.8 2928.9 —^(b) ^(a)Arithmetic mean ^(b)Controls treated

As can be seen from the data shown on Table I, the gel composition ofthe invention provides significantly increased efficacy for a greaterperiod of time than a comparable commercially available pastecomposition.

EXAMPLE 3

Evaluation of the Endoparasiticidal Efficacy of Composition A

In this evaluation a group of 12 horses are treated orally with a doseof 0.4 mg/kg moxidectin and 2.5 mg/kg praziquantel (Composition A) and agroup of 12 horses are left untreated (Control). Two weeks posttreatment, parasite burdens are determined and % efficacy for treatedanimals is calculated. The data are averaged. The results are shown inTable II.

Parasites Column Heading Scientific Name G. intest. G. intestinalis G.nasalis G. nasalis Paranopl. Paranoplocchphila Anoplo. Spp.Anoplocephala Spp.

TABLE II Evaluation of Endoparasiticidal Efficacy % Efficacy G. intest.G. nasalis Paranopl. Anoplo. Spp. Treatment (12/12)^(a) (12/12) (10/12)(12/12) Comp. A 96.7 98.8 99.1 100.0 Control^(b) 201.8 136.5 11.2 6.7^(a)Number infected/total ^(b)Geometric means parasite (degree ofinfection)

As can be seen from the data on Table II, the gel composition of theinvention demonstrates a high degree of efficacy over a broad spectrumof endoparasites.

EXAMPLE 4

Efficacy of Gel Formulation

Twenty-six New Forest cross male ponies approximately 1-2 years of agewere used in this study. All were sourced from an area of the New Foreston which animals known to be infected with Gasterophilus spp. and A.perfoliata had grazed. This had been assessed by post-mortem examinationof material at a horse abattoir in South West England carried out beforethe trial.

The horses were housed in small groups of 4-6 for 18 days prior totreatment. Each horse was given a physical examination by a veterinarysurgeon to determine its suitability for use in the trial. Post-mortemexamination of two randomly selected tracer animals seven days prior totreatment revealed moderate burdens of P. mamillana and A. perfoliata,as well as moderate to heavy burdens of both the L2 and L3 instars of G.intestinalis and G. nasalis.

The remaining 24 animals were ranked in order of increasing bodyweight,to form 12 pairs, then allocated at random to either untreated controlor to moxidectin/praziquantel gel groups. The latter was administered ata rate of 0.5 ml/25 kg bodyweight to provide 0.4 mg moxidectin/kg and2.5 mg praziquantel/kg bodyweight. Treatment consisted of a single oraladministration into the back of the mouth at the base of the tongue. Theanimals were treated using pre-filled syringes graduated to the nearest25 kg. The syringes were weighed before and after treatment to determinethe actual dose given.

On days 13-14 post-treatment all animals were necropsied and their botand tapeworm burdens determined. Faecal samples were collected 14 daysprior to treatment and at time of necropsy on day 13-14 post-treatmentand examined for the presence of tapeworm eggs and strongyle eggs usinga modified McMaster flotation technique. At necropsy thegastrointestinal tract from stomach to large intestine was removed anddivided by ligature into stomach, small intestine, caecum, ventral anddorsal colon, for separate processing.

Gasterophilus spp larvae present on the gastric mucosa and in thestomach contents were removed for enumeration. Identification ofindividual species and instar was carried out according to the keydescribed in Wells and Knipling (1937).

Each section of the intestines was opened and the contents collected.Any visible tapeworms remaining on the intestinal wall were similarlyremoved for identification and counting. Identification of individualtapeworm species was carried out according to predilection site, sizeand other morphological features. A bulk faecal sample from theuntreated control group collected at necropsy was cultured to identifythe species/genus of nematode present.

Bot and tapeworm counts were transformed by Y=In (count+1)transformation prior to analysis. The two groups were compared using atwo-way analysis of variance with the level of significance set at the5% level. The moxidectin/praziquantel combination equine gel formulationwas determined to have activity against a specific species of parasiteif each of the following three conditions were met:

-   1. the efficacy equals or exceeds 90% as determined by the geometric    mean;-   2. at least six control animals are infected with the same parasite    species; and-   3. the treatment effect is significant at the P<0.05 level.    Results

No adverse effects were observed in any of the treated animals aftertreatment. The gel formulation also appeared to be palatable. Apart fromone horse, which accidentally ingested twice the recommended dosethrough biting on the syringe, the actual dose administered ranged from94 to 102 (mean 99) % of the target dose.

All 24 ponies had positive strongyle eggs counts prior to treatment. Eggcounts ranged from 60-1050 with a mean of 252 eggs per gram (EPG). Aftertreatment, the figures were 288 (range 0-980) epg for the controls and0.3 epg (one positive animal) for the treated group, representing areduction of 99.9%. Coproculture of pooled faeces from the control groupat slaughter revealed that the strongyle population was composed of 68%Cyathostoma spp. and 32% Strongylus spp.

All 12 controls carried A. perfoliata burdens at necropsy, as shown inTable III. Numbers ranged from 1-36 with a geometric mean of 6.7. Incontrast, the treated group had zero counts. Ten out of the 12 ponieswere also infected with P. mamillana (mean 11.2, range 1 to 133),whereas in the treated group a single tapeworm was found in one animalonly (mean 0.1) giving an efficacy figure of 99.9% (P<0.001). No A.magna were found in any of the horses. Faecal examination failed todetect any tapeworm eggs in any of the animals either before or aftertreatment. This reflects the lack of sensitivity of the McMasterflotation technique for determining the presence of tapeworm eggs infaeces.

All the control animals were found to be infected with G. intestinalisand G. nasalis. Both the L2 and L3 stages were present. For G.intestinalis, the numbers ranged from 13-278 (mean 91.9) and 2-312 (mean89.4) respectively. Corresponding figures for the treated group were0-24 (mean 2.3) and 0-17 (mean 3.9) giving % reduction figures of 97.5%(P<0.001) and 95.6% (P<0.001) for the L2 and L3 stages respectively. Thenumbers of G. nasalis in the controls ranged from 12-400 (mean 46.7) forL2 and 25-140 (mean 80.8) for L3. In the treated group the figures were0-10 (mean 1.4) and 0-8 (mean 0.3) giving 97% (P<0.001) and 99.6%(P<0.001) efficacy against the L2 and L3 stages respectively.

The results of this study confirm that moxidectin/praziquantel equinegel at 0.4 mg moxidectin/kg and 2.5 mg praziquantel/kg bodyweight ishighly effective against tapeworms and bots in naturally infected horsesin the UK. It was 99-100% effective against A. perfoliata and P.mamillana and 95.6-99.6% effective against the L2 and L3 instars of G.intestinalis and G. nasalis. The product was well tolerated and wasaccepted by the animals. The 99.9% reduction in strongyle faecal eggcounts suggests that moxidectin, in conjunction with praziquantel,continues to have excellent activity against gastro-intestinalnematodes.

TABLE III Mean Tapeworm and bot counts at Necropsy Control Treated %Efficacy Number of Animals 12   12   A perfoliata  6.7 0   100 (1-36)(—) P. mamillana 11.2 0.1 99.1  (1-133) (0-1)  G. intestinalis L2 91.92.3 (13-278) (0-24) 97.5 L3 89.4 3.9  (2-312) (0-17) 95.6 G. nasalis L246.7 1.4 (12-400) (0-10) 97.0 L3 80.8 0.3 (25-140) (0-8)  99.6

EXAMPLE 5

A two part field study included a total of 43 horses for the nematodepart (I) and another 8 horses for the tape worm part (II). Part I: GroupA (N=26) was treated with the moxidectin/praziquantel gel, Group B(N=10) received an abamectin/praziquantel paste and 9 horses in Group Cremained as an untreated control group. The efficacy was monitored byfaecal egg per gram (epg) measurement: the average challenge in theGroup C ranged from 773.3 to 2928.9 epg. When following a commonrecommendation to treat when 50% of horses in the group have epg≧200,the horses in Group B would have had to be treated between week 6 and 8,when 6 out of 8 horses sampled had epg≧200. Group A horses did notwarrant a treatment at any time during the 14 week study period. Group Chad to be treated at week 12 for animal welfare reasons. Efficacyagainst tapeworm was 100%. A safety study in 14 young foals from 3 weeksto 7 weeks of age showed moxidectin 2%/praziquantel 12.5% horse gel tobe safe when applied up to 3 times recommended dose rate.

1. An endoparasiticidal gel composition which comprises: about 1.0% to3.5% wt/wt of moxidectin; about 10.0% to 15.0% wt/wt of praziquantel;about 4.0% to 24.0% wt/wt of benzyl alcohol; about 1.0% to 34.0% wt/wtof ethanol; about 2.0% to 15.0% wt/wt of colloidal silicon dioxide;about 1.0% to 20.0% wt/wt of a surfactant; and about 35.0% to 61.0%wt/wt of an oil, wherein said composition is an oral gel.
 2. Thecomposition according to claim 1 wherein the oil is propylene glycoldicaprylate/dicaprate or dicaprylic/dicapric triglyceride.
 3. Thecomposition according to claim 1 wherein moxidectin is present at about1.5% to 2.5% wt/wt.
 4. The composition according to claim 1 whereinpraziquantel is present at about 12.0% to 13.0% wt/wt.
 5. Thecomposition according to claim 1 wherein benzyl alcohol is present atabout 18.0% to 22.0% wt/wt.
 6. The composition according to claim 1wherein ethanol is present at about 5.0% to 7.5% wt/wt.
 7. Thecomposition according to claim 5 wherein the surfactant is present atabout 3.0% to 6.0%.
 8. The composition according to claim 7 wherein thesurfactant comprises a polyoxyethylene sorbitan ester.
 9. Thecomposition according to claim 8 wherein ethanol is present at about5.0% to 7.5% wt/wt.
 10. The composition according to claim 9 wherein theoil is propylene glycol dicaprylate/dicaprate.
 11. The compositionaccording to claim 10 wherein moxidectin is present at about 1.9% to2.0% wt/wt and praziquantel is present at about 12.0% to 12.5% wt/wt.